1. Field of the Invention
The present invention relates to a sputtering target and a manufacturing method thereof. In addition, the present invention relates to an oxide film formed by a sputtering method with use of the sputtering target, and a semiconductor device including the oxide film.
In this specification, a semiconductor device generally refers to a device which can function by utilizing semiconductor characteristics; an electro-optical device, a semiconductor circuit, and an electronic device are all included in the category of the semiconductor device.
2. Description of the Related Art
A technique by which transistors are formed using semiconductor thin films formed over a substrate having an insulating surface has been attracting attention. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). A silicon film is widely known as a semiconductor thin film applicable to the transistor. As another material, an oxide semiconductor film has been attracting attention.
For example, a transistor including an amorphous oxide semiconductor film that contains indium (In), gallium (Ga), and zinc (Zn) and has an electron carrier concentration less than 1018/cm3 is disclosed. As a method for forming the amorphous oxide semiconductor film, a sputtering method is considered the most suitable (see Patent Document 1).
Although a transistor including an oxide semiconductor film containing a plurality of metal elements can obtain transistor characteristics relatively with ease, the oxide semiconductor film is likely to be amorphous and has unstable physical properties. Thus, it is has been difficult to secure reliability of such a transistor.
On the other hand, there is a report that a transistor including a crystalline oxide semiconductor film has more excellent electric characteristics and higher reliability than a transistor including an amorphous oxide semiconductor film (see Non-Patent Document 1).